Electronic screening for image reproduction is well known in the art. According to a well known technique described in U.S. Pat. No. 4,456,924 of the present assignee, for each screened dot, a multiplicity of coordinates of a laser plotter are translated into screen-cell coordinates. A corresponding cell memory is preloaded by threshold values, defining a cell memory matrix. Input digitized scanned density values of an image, such as a color separation, are compared with the threshold values, cell by cell. The results provide an on/off control input for a laser plotter.
U.S. Pat. No. 4,149,183 describes an electronic halftone generator wherein a halftone signal is generated by pulse width modulating or comparing the scanned or video signal with a periodic analog signal having two frequencies and phases to create a dot pattern output which is a function of the frequency and phase of the two combined modulating signals. The halftone reproduction generated has variable dot configurations that are controllable to enable both rotation of the dot pattern and geometric modifications of the dot pattern.
U.S. Pat. No. 5,079,721 of the present assignee/applicant describes apparatus and a technique for generating a screened reproduction of an image comprising the steps of providing a representation of an original having input density values representing the grey levels of various locations of the original for a given color separation, defining a desired screen dot arrangement for the image, writing screen dots in a line by line fashion, wherein each screen dot is made up of a plurality of lines whose length and location determines the dot configuration and whose length and location is determined by an analog operation employing the input density values of the original and the desired screen dot arrangement.
U.S. Pat. No. 4,040,094 describes a method and apparatus for electronic screening of a graphic image to be reproduced by printing. The density of the graphic image is determined repetitively during the digital generation of each dot which will form a part of the half-tone image when produced, and the dot is modified according to changes in the density. Thus the structure of any halftone dot may be modified during its construction.